1. Field of the Invention
The present invention relates to an ink-jet head having nozzle openings through which ink droplets are discharged and manufacturing method thereof.
2. Description of the Prior Art
Improvements in recording density result in an increasingly dense array of nozzle openings. For this reason, there has been a demand for nozzle openings arrayed with high accuracy as well as for nozzle openings having high dimensional accuracy. Means for solving such a problem are disclosed in, for example, Japanese Patent Publication No. Hei. 6-55733. It proposes that ink cavities, an ink reservoir for feeding ink to the ink cavities, and an ink supply port for connecting the ink cavities to the ink reservoir be formed in a silicon monocrystalline substrate by anisotropic etching, and that a nozzle plate, in which nozzle openings are formed by anisotropically etching a silicon monocrystalline substrate having a face (100), and the silicon monocrystalline substrate be bonded into an integrally formed ink-jet recording head.
The article entitled "Continuous Ink-jet Print Head Utilizing Silicon Micromachined Nozzles" in "Sensors and Actuators A", 43 (1994), pp. 311-316, discloses a method of manufacturing a nozzle plate for use with an ink-jet printer. According to this method, boron is diffused into designated areas of a silicon monocrystalline substrate having a (100) face where nozzle openings are to be formed. The areas into which boron was diffused are selectively etched, whereby a plurality of nozzle openings are formed.
As previously described, the technique disclosed in Japanese Patent Publication No. Hei. 6-55733 uses the silicon monocrystalline substrate having a (100) face. If the silicon monocrystalline substrate is anisotropically etched, nozzle openings J, each consisting of four planes E, F, G, and H at an angle of 45.degree. with respect to the face (100), are recessed in the silicon monocrystalline substrate which constitutes a nozzle plate D, as shown in FIG. 9 (here reference symbol N designates a spacer which forms ink cavities K, ink supply ports L, and an ink reservoir M, and P designates a vibrating plate having pressure generating means Q formed therein).
If through-holes are formed in the face (100) of the silicon monocrystalline substrate by anisotropic etching, a ratio of a side length of the maximum opening of the through-hole to the thickness of the substrate becomes 2:1, as is well known. For this reason, it is necessary to limit the thickness of the silicon monocrystalline substrate to about 70 .mu.m in order to form nozzle openings at a density of 180 DPI or thereabouts.
To form ink dots having a size suitable for a printing operation, it is necessary for the minimum opening of the discharge orifice to have a diameter of 30 .mu.m. Allowing for the accuracy of formation of patterns used for arraying the nozzle openings, it is also necessary to ensure a pitch of about 10 .mu.m between the patterns. Because of these requirements, a silicon monocrystalline substrate which is considerably as thin as 30 .mu.m or thereabouts becomes necessary.
Even in the case of a silicon monocrystalline substrate having a diameter of about 100 mm (a 4-inch wafer), it is very difficult to cut that substrate to a thickness of about 30 .mu.m. Further, the rigidity of a sliced silicon monocrystalline substrate becomes extremely low, and hence it becomes very difficult to bond the substrate to another element, which in turn complicates manufacturing steps.
According to the technique disclosed in the article entitled "Sensors and Actuators A", the boron-diffused areas are etched. The depth to which boron can be diffused is, at most, 2-3 .mu.m or thereabouts, which makes a handling operation for bonding the substrate to another element considerably difficult. Hence, this technique is impossible to use from an industrial point of view.